Structure and formation method of semiconductor device with isolation structure

ABSTRACT

A semiconductor device structure and a method for forming a semiconductor device structure are provided. The semiconductor device structure includes a semiconductor fin over a substrate and multiple semiconductor nanostructures suspended over the semiconductor fin. The semiconductor device structure also includes a gate stack extending across the semiconductor fin, and the gate stack wraps around each of the semiconductor nanostructures. The semiconductor device structure further includes a first epitaxial structure and a second epitaxial structure sandwiching the semiconductor nanostructures. Each of the first epitaxial structure and the second epitaxial structure extends exceeding a top surface of the semiconductor fin. In addition, the semiconductor device structure includes an isolation structure between the semiconductor fin and the gate stack. The isolation structure further extends exceeding opposite sidewalls of the first epitaxial structure.

PRIORITY CLAIM AND CROSS-REFERENCE

This Application claims the benefit of U.S. Provisional Application No. 62/928,654, filed on Oct. 31, 2019, the entirety of which is incorporated by reference herein.

BACKGROUND

The semiconductor integrated circuit (IC) industry has experienced rapid growth. Technological advances in IC materials and design have produced generations of ICs. Each generation has smaller and more complex circuits than the previous generation.

Over the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometric size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling-down process generally provides benefits by increasing production efficiency and lowering associated costs.

However, these advances have increased the complexity of processing and manufacturing ICs. Since feature sizes continue to decrease, fabrication processes continue to become more difficult to perform. Therefore, it is a challenge to form reliable semiconductor devices at smaller and smaller sizes.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It should be noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIGS. 1A-1B are top views of various stages of a process for forming a semiconductor device structure, in accordance with some embodiments.

FIGS. 2A-2I are cross-sectional views of various stages of a process for forming a semiconductor device structure, in accordance with some embodiments.

FIGS. 3A-3K are cross-sectional views of various stages of a process for forming a semiconductor device structure, in accordance with some embodiments.

FIGS. 4A-4E are cross-sectional views of various stages of a process for forming a semiconductor device structure, in accordance with some embodiments.

FIGS. 5A-5C are cross-sectional views of various stages of a process for forming a semiconductor device structure, in accordance with some embodiments.

FIGS. 6A-6C are cross-sectional views of various stages of a process for forming a semiconductor device structure, in accordance with some embodiments.

FIG. 7 is a cross-sectional view of a semiconductor device structure, in accordance with some embodiments.

FIG. 8 is a cross-sectional view of a semiconductor device structure, in accordance with some embodiments.

FIG. 9 is a cross-sectional view of a semiconductor device structure, in accordance with some embodiments.

FIG. 10 is a cross-sectional view of a semiconductor device structure, in accordance with some embodiments.

FIG. 11 is a cross-sectional view of a semiconductor device structure, in accordance with some embodiments.

FIG. 12 is a cross-sectional view of a semiconductor device structure, in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

The term “substantially” in the description, such as in “substantially flat” or in “substantially coplanar”, etc., will be understood by the person skilled in the art. In some embodiments the adjective substantially may be removed. Where applicable, the term “substantially” may also include embodiments with “entirely”, “completely”, “all”, etc. Where applicable, the term “substantially” may also relate to 90% or higher, such as 95% or higher, especially 99% or higher, including 100%. Furthermore, terms such as “substantially parallel” or “substantially perpendicular” are to be interpreted as not to exclude insignificant deviation from the specified arrangement and may include for example deviations of up to 10°. The word “substantially” does not exclude “completely” e.g. a composition which is “substantially free” from Y may be completely free from Y.

Terms such as “about” in conjunction with a specific distance or size are to be interpreted so as not to exclude insignificant deviation from the specified distance or size and may include for example deviations of up to 10%. The term “about” in relation to a numerical value x may mean x±5 or 10%.

Embodiments of the disclosure may relate to FinFET structure having fins. The fins may be patterned using any suitable method. For example, the fins may be patterned using one or more photolithography processes, including double-patterning or multi-patterning processes. Generally, double-patterning or multi-patterning processes combine photolithography and self-aligned processes, allowing patterns to be created that have, for example, pitches smaller than what is otherwise obtainable using a single, direct photolithography process. For example, in some embodiments, a sacrificial layer is formed over a substrate and patterned using a photolithography process. Spacers are formed alongside the patterned sacrificial layer using a self-aligned process. The sacrificial layer is then removed, and the remaining spacers may then be used to pattern the fins. However, the fins may be formed using one or more other applicable processes.

Embodiments of the disclosure may relate to the gate all around (GAA) transistor structures. The GAA structure may be patterned using any suitable method. For example, the structures may be patterned using one or more photolithography processes, including double-patterning or multi-patterning processes. In some embodiments, double-patterning or multi-patterning processes combine photolithography and self-aligned processes, allowing patterns to be created that have, for example, pitches smaller than what is otherwise obtainable using a single, direct photolithography process. For example, in some embodiments, a sacrificial layer is formed over a substrate and patterned using a photolithography process. Spacers are formed alongside the patterned sacrificial layer using a self-aligned process. The sacrificial layer is then removed, and the remaining spacers may then be used to pattern the GAA structure.

Some embodiments of the disclosure are described. Additional operations can be provided before, during, and/or after the stages described in these embodiments. Some of the stages that are described can be replaced or eliminated for different embodiments. Additional features can be added to the semiconductor device structure. Some of the features described below can be replaced or eliminated for different embodiments. Although some embodiments are discussed with operations performed in a particular order, these operations may be performed in another logical order.

FIGS. 2A-2I are cross-sectional views of various stages of a process for forming a semiconductor device structure, in accordance with some embodiments. As shown in FIG. 2A, a semiconductor substrate 100 is received or provided. The semiconductor substrate 100 has a first region 10 and a second region 20. In some embodiments, one or more short channel (SC) devices are to be formed over the first region 10. One or more long channel (LC) devices are to be formed over the second region 20. In some embodiments, the semiconductor substrate 100 is a bulk semiconductor substrate, such as a semiconductor wafer. The semiconductor substrate 100 may include silicon or other elementary semiconductor materials such as germanium. The semiconductor substrate 100 may be un-doped or doped (e.g., p-type, n-type, or a combination thereof). In some embodiments, the semiconductor substrate 100 includes an epitaxially grown semiconductor layer on a dielectric layer. The epitaxially grown semiconductor layer may be made of silicon germanium, silicon, germanium, one or more other suitable materials, or a combination thereof.

In some other embodiments, the semiconductor substrate 100 includes a compound semiconductor. For example, the compound semiconductor includes one or more III-V compound semiconductors having a composition defined by the formula Al_(X1)Ga_(X2)In_(X3)As_(Y1)P_(Y2)N_(Y3)Sb_(Y4), where X1, X2, X3, Y1, Y2, Y3, and Y4 represent relative proportions. Each of them is greater than or equal to zero, and added together they equal 1. The compound semiconductor may include silicon carbide, gallium arsenide, indium arsenide, indium phosphide, one or more other suitable compound semiconductors, or a combination thereof. Other suitable substrate including II-VI compound semiconductors may also be used.

In some embodiments, the semiconductor substrate 100 is an active layer of a semiconductor-on-insulator (SOI) substrate. The SOI substrate may be fabricated using a separation by implantation of oxygen (SIMOX) process, a wafer bonding process, another applicable method, or a combination thereof. In some other embodiments, the semiconductor substrate 100 includes a multi-layered structure. For example, the semiconductor substrate 100 includes a silicon-germanium layer formed on a bulk silicon layer.

As shown in FIG. 2A, a semiconductor stack having multiple semiconductor layers is formed over the semiconductor substrate 100, in accordance with some embodiments. The semiconductor stack covers the first region 10 and the second region 20 of the semiconductor substrate 100. In some embodiments, the semiconductor stack includes multiple semiconductor layers 102 a, 102 b, 102 c, and 102 d, and the semiconductor stack also includes multiple semiconductor layers 104 a, 104 b, 104 c, and 104 d. In some embodiments, the semiconductor layers 102 a-102 d and the semiconductor layers 104 a-104 d are laid out alternately, as shown in FIG. 2A.

In some embodiments, the semiconductor layer 102 a is used as a sacrificial base layer and will be partially or completely removed in a subsequent process. In some embodiments, the semiconductor layer 104 a functions as a protective layer that prevents the semiconductor layer 102 b thereon from being damaged during the subsequent fabrication processes. In some embodiments, the semiconductor layers 102 b-102 d function as sacrificial layers that will be removed in a subsequent process to release the semiconductor layers 104 b-104 d. The released semiconductor layers 104 b-104 d may function as channel structures of one or more transistors.

In some embodiments, the semiconductor layer 104 a is thinner than the semiconductor layer 104 b, 104 c, or 104 d. As shown in FIG. 2A, the semiconductor layer 104 a has a thickness T₁, and the semiconductor layer 104 b has a thickness T₂. In some embodiments, the thickness T₂ is greater than the thickness T₁. The thickness T₁ may be in a range from about 2 nm to about 6 nm. For example, the thickness T₁ is about 4 nm. The ratio (T₁/T₂) of the thickness T₁ to the thickness T₂ may be in a range from about 2/5 to about 2/3. In some other embodiments, the ratio (T₁/T₂) of the thickness T₁ to the thickness T₂ is in a range from about 3/5 to about 3/4. The ratio (T₁/T₂) will be discussed in more detail later.

In some embodiments, each of the semiconductor layers 102 b-102 d and 104 b-104 d has substantially the same thickness. In some embodiments, each of the semiconductor layers 104 b-104 d is thicker than each of the semiconductor layers 102 a-102 d. In some other embodiments, each of the semiconductor layers 102 a-102 d is thicker than each of the semiconductor layers 104 b-104 d.

In some embodiments, the semiconductor layer 102 a (that functions as a sacrificial base layer) is thicker than or substantially as thick as the semiconductor layer 102 b, 102 c, or 102 d (that functions as a sacrificial layer). As shown in FIG. 2A, the semiconductor layer 102 a has a thickness T₃, and the semiconductor layer 102 b has a thickness T₄. In some embodiments, the thickness T₃ is greater than the thickness T₄. The thickness T₃ may be in a range from about 4 nm to about 10 nm. For example, the thickness T₃ is about 5 nm. The ratio (T₃/T₄) of the thickness T₃ to the thickness T₄ may be in a range from about 1 to about 2. In some other embodiments, the ratio (T₃/T₄) of the thickness T₃ to the thickness T₄ is in a range from about 1.1 to about 1.8. The ratio (T₃/T₄) will be discussed in more detail later.

In some embodiments, the semiconductor layers 102 a-102 d and the semiconductor layers 104 a-104 d are made of different materials. In some embodiments, the semiconductor layers 102 a-102 d are made of or include silicon germanium or germanium, and the semiconductor layers 104 a-104 d are made of or include silicon.

In some embodiments, the semiconductor layer 102 a has a different atomic concentration of germanium than that of the semiconductor layer 102 b, 102 c, or 102 d. In some embodiments, the semiconductor layer 102 a has a greater atomic concentration of germanium than that of the semiconductor layer 102 b, 102 c, or 102 d. The atomic concentration of germanium of the semiconductor layer 102 a may be in a range from about 35% to about 50%. The atomic concentration of germanium of the semiconductor layer 102 b, 102 c, or 102 d may be in a range from about 15% to about 25%. The greater atomic concentration of germanium of the semiconductor layer 102 a enables the semiconductor layer 102 a to have different etching selectivity to the semiconductor layers 102 b, 102 c, and 102 d.

In some embodiments, the semiconductor layers 102 a-102 d and the semiconductor layers 104 a-104 d are formed using multiple epitaxial growth operations. Each of the semiconductor layers 102 a-102 d and the semiconductor layers 104 a-104 d may be formed using a selective epitaxial growth (SEG) process, a CVD process (e.g., a vapor-phase epitaxy (VPE) process, a low-pressure chemical vapor deposition (LPCVD) process, and/or an ultra-high vacuum CVD (UHV-CVD) process), a molecular beam epitaxy process, one or more other applicable processes, or a combination thereof.

In some embodiments, the semiconductor layers 102 a-102 d and the semiconductor layers 104 a-104 d are grown in-situ in the same process chamber. In some embodiments, the growth of the semiconductor layers 102 a-102 d and the growth of the semiconductor layers 104 a-104 d are alternately and sequentially performed in the same process chamber to complete the formation of the semiconductor stack. In some embodiments, the vacuum of the process chamber is not broken before the epitaxial growth of the semiconductor stack is accomplished.

Afterwards, hard mask elements are formed over the semiconductor stack to assist in a subsequent patterning of the semiconductor stack. One or more etching processes are used to pattern the semiconductor stack into fin structures 106A₁, 106A₂, 106B₁ and 106B₂, as shown in FIG. 2B in accordance with some embodiments. The fin structures 106A₁ and 106A₂ are formed over the first region 10, and the fin structures 106B₁ and 106B₂ are formed over the second region 20. The semiconductor stack is partially removed to form multiple trenches 112, as shown in FIG. 2B. Each of the fin structures 106A₁, 106A₂, 106B₁ and 106B₂ may include portions of the semiconductor layers 102 a-102 d and 104 a-104 d and semiconductor fin 101A₁, 101A₂, 101B₁ or 101B₂. The semiconductor substrate 100 may also be partially removed during the etching process for forming the fin structures 106A₁, 106A₂, 106B₁ and 106B₂. Protruding portions of the semiconductor substrate 100 that remain form the semiconductor fins 101A₁, 101A₂, 101B₁ and 101B₂.

Each of the hard mask elements used for patterning the semiconductor stack may include a first mask layer 108 and a second mask layer 110. The first mask layer 108 and the second mask layer 110 may be made of different materials. In some embodiments, the first mask layer 108 is made of a material that has good adhesion to the semiconductor layer 104 d. The first mask layer 108 may be made of silicon oxide, germanium oxide, silicon germanium oxide, one or more other suitable materials, or a combination thereof. In some embodiments, the second mask layer 110 is made of a material that has good etching selectivity to the semiconductor layers 102 a-102 d and 104 a-104 d. The second mask layer 110 may be made of silicon nitride, silicon oxynitride, silicon carbide, one or more other suitable materials, or a combination thereof.

FIGS. 1A-1B are top views of various stages of a process for forming a semiconductor device structure, in accordance with some embodiments. In some embodiments, the extending directions of the fin structures 106A₁, 106A₂, 106B₁ and 106B₂ are substantially parallel to each other, as shown in FIG. 1A. In some embodiments, FIG. 2B is a cross-sectional view of the structure taken along the lines 2B-2B and 2B′-2B′ in FIG. 1A.

As shown in FIG. 2C, an isolation feature 114 is formed to surround lower portions of the fin structures 106A₁, 106A₂, 106B₁ and 106B₂, in accordance with some embodiments. In some embodiments, one or more dielectric layers are deposited over the fin structures 106A₁, 106A₂, 106B₁ and 106B₂ and the semiconductor substrate 100 to overfill the trenches 112. The dielectric layers may be made of silicon oxide, silicon oxynitride, borosilicate glass (BSG), phosphoric silicate glass (PSG), borophosphosilicate glass (BPSG), fluorinated silicate glass (FSG), low-k material, porous dielectric material, one or more other suitable materials, or a combination thereof. The dielectric layers may be deposited using a flowable chemical vapor deposition (FCVD) process, an atomic layer deposition (ALD) process, a chemical vapor deposition (CVD) process, one or more other applicable processes, or a combination thereof.

Afterwards, a planarization process is used to partially remove the dielectric layers. The hard mask elements (including the first mask layer 108 and the second mask layer 110) may also function as a stop layer of the planarization process. The planarization process may include a chemical mechanical polishing (CMP) process, a grinding process, a dry polishing process, an etching process, one or more other applicable processes, or a combination thereof. Afterwards, one or more etching back processes are used to partially remove the dielectric layers. As a result, the remaining portion of the dielectric layers forms the isolation feature 114. Upper portions of the fin structures 106A₁, 106A₂, 106B₁ and 106B₂ protrude from the top surface of the isolation feature 114, as shown in FIG. 2C. Afterwards, the hard mask elements (including the first mask layer 108 and the second mask layer 110) are removed. Alternatively, in some other embodiments, the hard mask elements are removed or consumed during the planarization process and/or the etching back process.

Afterwards, dummy gate stacks 120A₁, 120A₂, 120B₁, and 120B₂ are formed to extend across the fin structures 106A₁, 106A₂, 106B₁ and 106B₂, as shown in FIG. 1B in accordance with some embodiments. In some embodiments, FIG. 2D is a cross-sectional view of the structure taken along the lines 2D-2D and 2D′-2D′ in FIG. 1B. FIGS. 3A-3K are cross-sectional views of various stages of a process for forming a semiconductor device structure, in accordance with some embodiments. In some embodiments, FIG. 3A is a cross-sectional view of the structure taken along the lines 3A-3A and 3A′-3A′ in FIG. 1B.

As shown in FIGS. 1B, 2D, and 3A, the dummy gate stacks 120A₁, 120A₂, 120B₁, and 120B₂ are formed to partially cover and to extend across the fin structures 106A₁, 106A₂, 106B₁ and 106B₂, in accordance with some embodiments. In some embodiments, the dummy gate stacks 120A₁ and 120A₂ wraps around the fin structures 106A₁ and 106A₂. The dummy gate stacks 120B₁ and 120B₂ wraps around the fin structures 106B₁ and 106B₂. As shown in FIG. 2D, the dummy gate stack 120A₂ extends across and wraps around the fin structures 106A₁ and 106A₂, and the dummy gate stack 120B₂ extends across and wraps around the fin structures 106B₁ and 106B₂.

In some embodiments, the device formed over the second region 20 has a longer channel width than the device formed over the first region 10. As shown in FIG. 1B, the device formed over the first region 10 has a channel width L_(SC), and the device formed over the second region 20 has a channel width L_(LC). The channel width L_(LC) is longer than the channel width L_(SC). The channel width L_(SC) may be in a range from about 4 nm to about 20 nm. The channel width L_(LC) may be in a range from about 22 nm to about 40 nm. As shown in FIG. 1B, the pitch P_(LC) between the dummy gate stacks 120B₁ and 120B₂ is longer than the pitch P_(SC) between the dummy gate stacks 120A₁ and 120A₂. The pitch P_(SC) may be in a range from about 15 nm to about 60 nm. The pitch P_(LC) may be in a range from about 65 nm to about 120 nm.

As shown in FIGS. 2D and 3A, each of the dummy gate stacks 120A₁, 120A₂, 120B₁, and 120B₂ includes a dummy gate dielectric layer 116 and a dummy gate electrode 118. The dummy gate dielectric layers 116 may be made of or include silicon oxide. The dummy gate electrodes 118 may be made of or include polysilicon. In some embodiments, a dummy gate dielectric material layer and a dummy gate electrode layer are sequentially deposited over the isolation feature 114 and the fin structures 106A₁, 106A₂, 106B₁ and 106B₂. The dummy gate dielectric material layer may be deposited using an ALD process, a CVD process, one or more other applicable processes, or a combination thereof. The dummy gate electrode layer may be deposited using a CVD process. Afterwards, the dummy gate dielectric material layer and the dummy gate electrode layer are patterned to form the dummy gate stacks 120A₁, 120A₂, 120B₁, and 120B₂.

In some embodiments, hard mask elements including mask layers 122 and 124 are used to assist in the patterning process for forming the dummy gate stacks 120A₁, 120A₂, 120B₁, and 120B₂. With the hard mask elements as an etching mask, one or more etching processes are used to partially remove the dummy gate dielectric material layer and the dummy gate electrode layer. As a result, remaining portions of the dummy gate dielectric material layer and the dummy gate electrode layer form the dummy gate dielectric layers 116 and the dummy gate electrodes 118 of the dummy gate stacks 120A₁, 120A₂, 120B₁, and 120B₂, respectively.

As shown in FIG. 3B, spacer layers 126 and 128 are afterwards deposited over the structure shown in FIG. 3A, in accordance with some embodiments. The spacer layers 126 and 128 extend along the sidewalls of the dummy gate stacks 120A₁, 120A₂, 120B₁, and 120B₂. The spacer layers 126 and 128 are made of different materials. The spacer layer 126 may be made of a dielectric material that has a low dielectric constant. The spacer layer 126 may be made of or include silicon carbide, silicon oxycarbide, silicon oxide, one or more other suitable materials, or a combination thereof. The spacer layer 128 may be made of a dielectric material that can provide more protection to the gate stacks during subsequent processes. The spacer layer 128 may have a greater dielectric constant than that of the spacer layer 126. The spacer layer 128 may be made of silicon nitride, silicon oxynitride, carbon-containing silicon nitride, carbon-containing silicon oxynitride, one or more other suitable materials, or a combination thereof. The spacer layers 126 and 128 may be sequentially deposited using a CVD process, an ALD process, a physical vapor deposition (PVD) process, one or more other applicable processes, or a combination thereof.

As shown in FIG. 3C, the spacer layers 126 and 128 are partially removed, in accordance with some embodiments. One or more anisotropic etching processes may be used to partially remove the spacer layers 126 and 128. As a result, remaining portions of the spacer layers 126 and 128 form spacer elements 126′ and 128′, respectively. The spacer elements 126′ and 128′ extend along the sidewalls of the dummy gate stacks 120A₁, 120A₂, 120B₁, and 120B₂, as shown in FIG. 3C.

The fin structures 106A₁, 106A₂, 106B₁ and 106B₂ are partially removed to form recesses 130 that are used to contain epitaxial structures (such as source/drain structures) that will be formed later. The recesses 130 expose the side surfaces of the semiconductor layers 102 a-102 d and 104 a-104 d.

One or more etching processes may be used to form the recesses 130. In some embodiments, a dry etching process is used to form the recesses 130. Alternatively, a wet etching process may be used to form the recesses 130. In some embodiments, each of the recesses 130 penetrates through the fin structure 106A₁ or 106B₁. In some embodiments, the recesses 130 further extend into the semiconductor fin (such as the semiconductor fin 101A₁ or 101B₁), as shown in FIG. 3C. The recesses 130 extend downwards to exceed the top surfaces of the semiconductor fins 101A₁ and 101B₁. In some embodiments, the spacer elements 126′ and 128′ and the recesses 130 are formed using the same etching process.

In some embodiments, each of the recesses 130 has slanted sidewalls. Upper portions of the recesses 130 are larger (or wider) than lower portions of the recesses 130. In these cases, due to the profile of the recesses 130, an upper semiconductor layer (such as the semiconductor layer 104 d) is shorter than a lower semiconductor layer (such as the semiconductor layer 104 b).

However, embodiments of the disclosure have many variations. In some other embodiments, the recesses 130 have substantially vertical sidewalls. In these cases, due to the profile of the recesses 130, an upper semiconductor layer (such as the semiconductor layer 104 d) is substantially as wide as a lower semiconductor layer (such as the semiconductor layer 104 b).

As shown in FIG. 3D, the semiconductor layers 102 b-102 d are laterally etched from the side surfaces of the semiconductor layers 102 b-102 d that are exposed by the recesses 130, in accordance with some embodiments. As a result, edges of the semiconductor layers 102 b-102 d retreat from edges of the semiconductor layers 104 a-104 d. As shown in FIG. 3D, recesses 132 are formed due to the lateral etching of the semiconductor layers 102 b-102 d. The recesses 132 may be used to contain inner spacers that will be formed later. The semiconductor layers 102 b-102 d may be laterally etched using a wet etching process, a dry etching process, or a combination thereof.

In some embodiments, the semiconductor layer 102 a (that functions as a sacrificial base layer) is completely or partially removed. In some embodiments, the semiconductor layer 102 a is completely removed to form recesses 133, as shown in FIGS. 3D and 2E. Due to the support of the dummy gate stacks 120A₁, 120A₂, 120B₁, and 120B₂ (as shown in FIG. 2E), the fin structures 106A₁, 106A₂, 106B₁ and 106B₂ are prevented from falling down even if the semiconductor layer 102 a is completely removed. In some embodiments, the semiconductor layer 102 a is simultaneously etched during the lateral etching of the semiconductor layers 102 b-102 d. In some embodiments, the semiconductor layers 102 a-102 d are etched using the same etching process. During the removal of the semiconductor layer 102 a, the semiconductor layer 104 a functions as a protective layer to prevent the semiconductor layer 102 b above from being etched or damaged from the bottom surface of the semiconductor layer 102 b.

As mentioned above, in some embodiments, the semiconductor layer 102 a (that function as a sacrificial base layer) is thicker than the semiconductor layer 102 b, 102 c, or 102 d (that functions as a sacrificial layer). As mentioned above, in some embodiments, the semiconductor layer 102 a has a greater atomic concentration of germanium than that of the semiconductor layer 102 b, 102 c, or 102 d. Because the semiconductor layer 102 a is thicker and/or has a greater atomic concentration of germanium, the semiconductor layer 102 a may be etched at a greater etching rate than the semiconductor layers 102 b-102 d. As a result, after the etching process, the semiconductor layer 102 a is completely removed to form the recesses 133 while the semiconductor layers 102 b-102 d are partially etched to form the recesses 132, as shown in FIG. 3D in accordance with some embodiments.

During the etching of the semiconductor layers 102 a-102 d, the semiconductor layers 104 a-104 d may also be slightly etched. As a result, edge portions of the semiconductor layers 104 b-104 d are partially etched and thus shrink to become edge elements 105 b-105 d, as shown in FIG. 3D. As shown in FIG. 3D, each of the edge elements 105 b-105 d of the semiconductor layers 104 b-104 d is thinner than the corresponding inner portion of the semiconductor layers 104 b-104 d. In some embodiments, since the semiconductor layer 104 a is thinner than each of the semiconductor layers 104 b-104 d, no edge portion is formed beside the semiconductor layer 104 a. As shown in FIGS. 3D and 2E, the semiconductor layer 104 a becomes thinner after the formation the recesses 133, in accordance with some embodiments.

As shown in FIG. 3E, a spacer layer 134 is deposited over the structure shown in FIG. 3D, in accordance with some embodiments. The spacer layer 134 covers the dummy gate stacks 120A₁, 120A₂, 120B₁, and 120B₂ and fills the recesses 132 and 133. The spacer layer 134 may be made of or include carbon-containing silicon nitride (SiCN), carbon-containing silicon oxynitride (SiOCN), carbon-containing silicon oxide (SiOC), one or more other suitable materials, or a combination thereof. The spacer layer 134 may be deposited using a CVD process, an ALD process, one or more other applicable processes, or a combination thereof.

As shown in FIG. 3E, the portion of the spacer layer 134 over the first region 10 has a thickness T₅ at the bottom of the recess 130, and the portion of the spacer layer 134 over the second region 20 has a thickness T₆ at the bottom of the recess 130. In some embodiments, the thickness T₅ is greater than the thickness T₆. Due to the smaller pitch between the dummy gate stacks over the first region 10, the recess 130 over the first region 10 is narrower than the recess 130 over the second region 20. Therefore, the deposited material used for forming the spacer layer 134 may accumulate at the bottom of the recess 130 over the first region 10 at a higher deposition rate.

As shown in FIG. 3F, an etching process is used to partially remove the spacer layer 134, in accordance with some embodiments. In some embodiments, first remaining portions of the spacer layer 134 in the recesses 132 form inner spacers 136, as shown in FIG. 3F. In some embodiments, second remaining portions of the spacer layer 134 filling the recesses 133 and filling some of the recesses 132 form isolation structures 137A₁, 137A₂, 137B₁, 137B₁′, and 137B₂′, as shown in FIGS. 3F and 2F. In some embodiments, the inner spacers 136 and the isolation structures 137A₁, 137A₂, 137B₁, 137B₁′, and 137B₂′ are made of the same material. The etching process used for the partial removal of the spacer layer 134 may include a dry etching process, a wet etching process, or a combination thereof.

The inner spacers 136 and the isolation structures 137A₁, 137B₁, and 137B₁′ cover the edges of the semiconductor layers 102 b-102 d that are originally exposed by the recesses 132, as shown in FIG. 3F. The inner spacers 136 and the isolation structures 137A₁, 137B₁, and 137B₁′ may be used to prevent subsequently formed epitaxial structures (that function as, for example, source/drain structures) from being damaged during a subsequent removing process of the semiconductor layers 102 b-102 d. The inner spacers 136 and the isolation structures 137A₁, 137B₁, and 137B₁′ may also be used to reduce parasitic capacitance between the subsequently formed source/drain structures and the gate stacks. The isolation structures 137A₁, 137A₂, 137B₁, 137B₁′, and 137B₂′ may help to reduce or prevent current leakage from the subsequently formed epitaxial structures. Therefore, the operation speed and reliability of the semiconductor device structure may be improved.

As illustrated in some embodiments in FIG. 3C, the recesses 130 extend downwards to exceed the top surfaces of the semiconductor fins 101A₁ and 101B₁, which ensures that the side surfaces of the semiconductor layers 102 b-102 d are exposed. Therefore, during the lateral etching illustrated in FIG. 3D, each of the semiconductor layers 102 b-102 d is laterally etched with a sufficient amount. All of the recesses 132 are thus deep enough for containing the inner spacers 136 or portions of the isolation structures 137A₁, 137B₁, or 137B₁′. Each of the inner spacers 136 or the isolation structures 137A₁, 137B₁, or 137B₁′ is thus thick enough to provide sufficient protection to the subsequently formed epitaxial structures during a subsequent removing process of the semiconductor layers 102 b-102 d.

In some embodiments, after the etching process for forming the inner spacers 136, portions of the semiconductor fin 101B₁ originally covered by the spacer layer 134 are exposed by the recesses 130, as shown in FIG. 3F. Meanwhile, the semiconductor fin 101A₁ remains being covered by isolation structure 137A₁ (that is a remaining portion of the spacer layer 134), as shown in FIG. 3F in accordance with some embodiments.

As shown in FIG. 3G, epitaxial structures 138 are formed beside the dummy gate stacks 120A₁, 120A₂, 120B₁, and 120B₂, in accordance with some embodiments. In some embodiments, the epitaxial structures 138 fill the recesses 130, as shown in FIG. 3G. In some other embodiments, the epitaxial structures 138 overfill the recesses 130. In these cases, the top surfaces of the epitaxial structures 138 may be higher than the top surface of the dummy gate dielectric layer 116. In some other embodiments, the epitaxial structures 138 partially fill the recesses 130. In some embodiments, the epitaxial structures 138 extend exceeding or past the top surfaces of the semiconductor fins 101A₁ and 101B₁.

In some embodiments, the epitaxial structures 138 connect to the semiconductor layers 104 b-104 d. Each of the semiconductor layers 104 b-104 d is sandwiched between two of the epitaxial structures 138. In some embodiments, the epitaxial structures 138 function as source/drain structures. In some embodiments, some of the epitaxial structures 138 are in direct contact with the semiconductor fin 101B₁, as shown in FIG. 3G. In some embodiments, some of the epitaxial structures 138 are separated from the semiconductor fin 101A₁ by the isolation structure 137A₁, as shown in FIG. 3G. In some embodiments, some of the epitaxial structures 138 are in direct contact with the isolation structure 137A₁.

In some embodiments, the epitaxial structures 138 are p-type doped regions. The epitaxial structures 138 may include epitaxially grown silicon germanium (SiGe), epitaxially grown silicon, or another suitable epitaxially grown semiconductor material. In some other embodiments, the epitaxial structures 138 are n-type doped regions. The epitaxial structures 138 may include epitaxially grown silicon, epitaxially grown silicon carbide (SiC), epitaxially grown silicon phosphide (SiP), or another suitable epitaxially grown semiconductor material. In some embodiments, some of the epitaxial structures 138 are p-type doped regions, and other epitaxial structures 138 are n-type doped regions.

In some embodiments, the epitaxial structures 138 are formed using a selective epitaxial growth (SEG) process, a CVD process (e.g., a vapor-phase epitaxy (VPE) process, a low-pressure chemical vapor deposition (LPCVD) process, and/or an ultra-high vacuum CVD (UHV-CVD) process), a molecular beam epitaxy process, one or more other applicable processes, or a combination thereof.

In some embodiments, the epitaxial structures 138 are doped with one or more suitable dopants. For example, the epitaxial structures 138 are SiGe source/drain features or Si source/drain features that are doped with boron (B), gallium (Ga), indium (In), carbon (C), phosphor (P), or another suitable dopant.

In some embodiments, the epitaxial structures 138 are doped in-situ during their epitaxial growth. The initial reaction gas mixture for forming the epitaxial structures 138 contains dopants. In some other embodiments, the epitaxial structures 138 are not doped during the growth of the epitaxial structures 138. Instead, after the formation of the epitaxial structures 138, the epitaxial structures 138 are doped in a subsequent process. In some embodiments, the doping is achieved by using an ion implantation process, a plasma immersion ion implantation process, a gas and/or solid source diffusion process, one or more other applicable processes, or a combination thereof. In some embodiments, the epitaxial structures 138 are further exposed to one or more annealing processes to activate the dopants. For example, a rapid thermal annealing process is used.

As shown in FIG. 3H, a contact etch stop layer 139 and a dielectric layer 140 are formed to cover the epitaxial structures 138 and to surround the dummy gate stacks 120A₁, 120A₂, 120B₁, and 120B₂, in accordance with some embodiments. The contact etch stop layer 139 may be made of or include silicon nitride, silicon oxynitride, silicon carbide, aluminum oxide, one or more other suitable materials, or a combination thereof. The dielectric layer 140 may be made of or include silicon oxide, silicon oxynitride, borosilicate glass (BSG), phosphoric silicate glass (PSG), borophosphosilicate glass (BPSG), fluorinated silicate glass (FSG), low-k material, porous dielectric material, one or more other suitable materials, or a combination thereof.

In some embodiments, an etch stop material layer and a dielectric material layer are sequentially deposited over the structure shown in FIG. 3G. The etch stop material layer may be deposited using a CVD process, an ALD process, a PVD process, one or more other applicable processes, or a combination thereof. The dielectric material layer may be deposited using an FCVD process, a CVD process, an ALD process, one or more other applicable processes, or a combination thereof.

Afterwards, a planarization process is used to partially remove the etch stop material layer and the dielectric material layer. As a result, the remaining portions of the etch stop material layer and the dielectric material layer form the contact etch stop layer 139 and the dielectric layer 140, respectively. The planarization process may include a CMP process, a grinding process, an etching process, a dry polishing process, one or more other applicable processes, or a combination thereof. In some embodiments, the mask layers 122 and 124 are removed during the planarization process. In some embodiments, after the planarization process, the top surfaces of the contact etch stop layer 139, the dielectric layer 140, and the dummy gate electrodes 118 are substantially coplanar.

As shown in FIGS. 2G and 31, the dummy gate electrodes 118 of the dummy gate stacks 120A₁, 120A₂, 120B₁, and 120B₂ are removed to form trenches 142A₁, 142A₂, 142B₁, and 142B₂, in accordance with some embodiments. The trenches 142A₁, 142A₂, 142B₁, and 142B₂ expose the dummy gate dielectric layer 116.

As shown in FIGS. 2H and 3J, the dummy gate dielectric layer 116 and the semiconductor layers 102 b-102 d (that function as sacrificial layers) are removed to form recesses 144, in accordance with some embodiments. In some embodiments, an etching process is used to remove the semiconductor layers 102 b-102 d. Due to high etching selectivity, the semiconductor layers 104 b-104 d are slightly (or substantially not) etched. The remaining portions of the semiconductor layers 104 b-104 d form multiple semiconductor nanostructures 104 b′-104 d′ of the fin structures 106A₁, 106A₂, 106B₁ and 106B₂, as shown in FIGS. 2H and 3J. The semiconductor nanostructures 104 b′-104 d′ are constructed by or made up of the remaining portions of the semiconductor layer 104 b-104 d. The semiconductor nanostructures 104 b′-104 d′ suspended over the semiconductor fin 101A₁, 101A₂, 101B₁ or 101B₂ may function as channel structures of transistors.

As mentioned above, in some embodiments, the etchant used for removing the semiconductor layers 102 b-102 d also slightly removes the semiconductor layers 104 b-104 d that form the semiconductor nanostructures 104 b′-104 d′. As a result, the obtained semiconductor nanostructures 104 b′-104 d′ become thinner after the removal of the semiconductor layers 102 b-102 d. In some embodiments, each of the semiconductor nanostructures 104 b′-104 d′ is thinner than the edge portions 105 b-105 d, as shown in FIG. 3J. The edge portions 105 b-105 d are surrounded by other elements and thus are prevented from being reached and etched by the etchant.

In some embodiments, the etchant used for removing the semiconductor layers 102 b-102 d etches through the semiconductor layer 104 a that is thinner than the semiconductor layer 104 b, 104 c, or 104 d. As a result, the isolation structures 137A₁, 137A₂, 137B₁, 137B₁′, and 137B₂′ are exposed.

As mentioned above, after the removal of the semiconductor layers 102 b-102 d (that function as sacrificial layers), recesses 144 are formed. The recesses 144 connect to the trenches 142A₁, 142A₂, 142B₁, and 142B₂ and surround each of the semiconductor nanostructures 104 b′-104 d′. As shown in FIG. 3J, even if the recesses 144 between the semiconductor nanostructures 104 b′-104 d′ are formed, the semiconductor nanostructures 104 b′-104 d′ remain being held by the epitaxial structures 138. Therefore, after the removal of the semiconductor layers 102 b-102 d (that function as sacrificial layers), the released semiconductor nanostructures 104 b′-104 d′ are prevented from falling down.

During the removal of the semiconductor layers 102 b-102 d (that function as sacrificial layers), the inner spacers 136 and the isolation structures 137A₁, 137B₁, and 137B₁′ protect the epitaxial structures 138 from being etched or damaged. The quality and reliability of the semiconductor device structure are ensured.

As mentioned above, in some embodiments as illustrated in FIG. 2A, the ratio (T₁/T₂) of the thickness T₁ of the semiconductor layer 104 a (that afterwards functions as a protective layer to the semiconductor layer 102 b during the process illustrated in FIGS. 2E and 3D) to the thickness T₂ of the semiconductor layer 104 b (that afterwards becomes the nanostructure 104 b′) may be in a range from about 2/5 to about 2/3. In some cases, if the thickness ratio (T₁/T₂) is lower than about 2/5, the semiconductor layer 104 a with the thickness T₁ may be too thin. As a result, during the removal of the semiconductor layer 102 a (which function as sacrificial base layer) as illustrated IN FIGS. 2E and 3D, the semiconductor layer 104 a may be broken or completely removed, exposing the semiconductor layer 102 b above it to the etchant. The semiconductor layer 102 b may be damaged or removed. As a result, the spacer layer 134 that are formed later may occupy the space that is designed to contain the semiconductor layer 102 b. The subsequent processes may become hard to perform.

In some other cases, if the thickness ratio (T₁/T₂) is greater than about 2/3, the semiconductor layer 104 a with the thickness T₁ may be too thick. As a result, for removing the semiconductor layer 104 a, additional or heavier etching process may need to be used in the process illustrated in FIGS. 2H and 3J. The process time may become longer. The additional or heavier etching process may also damage other elements (such as the channel structures) that have been formed. The performance and reliability of the semiconductor device structure might be at a risk of being negatively affected.

As shown in FIGS. 2I and 3K, metal gate stacks 156A₁, 156A₂, 156B₁, and 156B₂ are formed to fill the trenches 142A₁, 142A₂, 142B₁, and 142B₂, in accordance with some embodiments. The metal gate stacks 156A₁, 156A₂, 156B₁, and 156B₂ extend into the recesses 144 to wrap around each of the semiconductor nanostructures 104 b′-104 d′. In some embodiments, each of the isolation structures 137A₁, 137A₂, 137B₁, 137B₁′, and 137B₂′ is in direct contact with the corresponding semiconductor fin 101A₁, 101A₂, 101B₁ or 101B₂, the corresponding epitaxial structure 138, and/or the corresponding metal gate stack 156A₁, 156A₂, 156B₁, and 156B₂, as shown in FIGS. 2I and 3K.

Each of the metal gate stacks 156A₁, 156A₂, 156B₁, and 156B₂ includes multiple metal gate stack layers. Each of the metal gate stacks 156A₁, 156A₂, 156B₁, and 156B₂ may include a gate dielectric layer 150, a work function layer 152, and a conductive filling 154. In some embodiments, the formation of the metal gate stacks 156A₁, 156A₂, 156B₁, and 156B₂ involves the deposition of multiple metal gate stack layers over the dielectric layer 140 to fill the trenches 142A₁, 142A₂, 142B₁, and 142B₂ and the recesses 144. The metal gate stack layers extend into the recesses 144 to wrap around each of the semiconductor nanostructures 104 b′-104 d′.

In some embodiments, the gate dielectric layer 150 is made of or includes a dielectric material with high dielectric constant (high-K). The gate dielectric layer 150 may be made of or include hafnium oxide, zirconium oxide, aluminum oxide, hafnium dioxide-alumina alloy, hafnium silicon oxide, hafnium silicon oxynitride, hafnium tantalum oxide, hafnium titanium oxide, hafnium zirconium oxide, one or more other suitable high-K materials, or a combination thereof. The gate dielectric layer 150 may be deposited using an ALD process, a CVD process, one or more other applicable processes, or a combination thereof.

In some embodiments, before the formation of the gate dielectric layer 150, an interfacial layers are formed on the surfaces of the semiconductor nanostructures 104 b′-104 d′. The interfacial layers are very thin and are made of, for example, silicon oxide or germanium oxide. In some embodiments, the interfacial layers are formed by applying an oxidizing agent on the surfaces of the semiconductor nanostructures 104 b′-104 d′. For example, a hydrogen peroxide-containing liquid may be applied or provided on the surfaces of the semiconductor nanostructures 104 b′-104 d′ so as to form the interfacial layers.

The work function layer 152 may be used to provide the desired work function for transistors to enhance device performance including improved threshold voltage. In some embodiments, the work function layer 152 is used for forming an NMOS device. The work function layer 152 is an n-type work function layer. The n-type work function layer is capable of providing a work function value suitable for the device, such as equal to or less than about 4.5 eV.

The n-type work function layer may include metal, metal carbide, metal nitride, or a combination thereof. For example, the n-type work function layer includes titanium nitride, tantalum, tantalum nitride, one or more other suitable materials, or a combination thereof. In some embodiments, the n-type work function layer is an aluminum-containing layer. The aluminum-containing layer may be made of or include TiAlC, TiAlO, TiAlN, one or more other suitable materials, or a combination thereof.

In some other embodiments, the work function layer 152 is used for forming a PMOS device. The work function layer 152 is a p-type work function layer. The p-type work function layer is capable of providing a work function value suitable for the device, such as equal to or greater than about 4.8 eV.

The p-type work function layer may include metal, metal carbide, metal nitride, other suitable materials, or a combination thereof. For example, the p-type metal includes tantalum nitride, tungsten nitride, titanium, titanium nitride, one or more other suitable materials, or a combination thereof.

The work function layer 152 may also be made of or include hafnium, zirconium, titanium, tantalum, aluminum, metal carbides (e.g., hafnium carbide, zirconium carbide, titanium carbide, aluminum carbide), aluminides, ruthenium, palladium, platinum, cobalt, nickel, conductive metal oxides, or a combinations thereof. The thickness and/or the compositions of the work function layer 152 may be fine-tuned to adjust the work function level.

The work function layer 152 may be deposited over the gate dielectric layer 150 using an ALD process, a CVD process, a PVD process, an electroplating process, an electroless plating process, one or more other applicable processes, or a combination thereof.

In some embodiments, a barrier layer is formed before the work function layer 152 to interface the gate dielectric layer 150 with the subsequently formed work function layer 152. The barrier layer may also be used to prevent diffusion between the gate dielectric layer 150 and the subsequently formed work function layer 152. The barrier layer may be made of or include a metal-containing material. The metal-containing material may include titanium nitride, tantalum nitride, one or more other suitable materials, or a combination thereof. The barrier layer may be deposited using an ALD process, a CVD process, a PVD process, an electroplating process, an electroless plating process, one or more other applicable processes, or a combination thereof.

In some embodiments, the conductive filling 154 are made of or include a metal material. The metal material may include tungsten, aluminum, copper, cobalt, one or more other suitable materials, or a combination thereof. A conductive layer used for forming the conductive filling 154 may be deposited over the work function layer 152 using a CVD process, an ALD process, a PVD process, an electroplating process, an electroless plating process, a spin coating process, one or more other applicable processes, or a combination thereof.

In some embodiments, a blocking layer is formed over the work function layer 152 before the formation of the conductive layer used for forming the conductive filling 154. The blocking layer may be used to prevent the subsequently formed conductive layer from diffusing or penetrating into the work function layer 152. The blocking layer may be made of or include tantalum nitride, titanium nitride, one or more other suitable materials, or a combination thereof. The blocking layer may be deposited using an ALD process, a PVD process, an electroplating process, an electroless plating process, one or more other applicable processes, or a combination thereof.

Afterwards, a planarization process is performed to remove the portions of the metal gate stack layers outside of the trenches 142A₁, 142A₂, 142B₁, and 142B₂, in accordance with some embodiments. As a result, the remaining portions of the metal gate stack layers form the metal gate stacks 156A₁, 156A₂, 156B₁, and 156B₂, as shown in FIGS. 2I and 3K.

In some embodiments, the conductive filling 154 does not extend into the recesses 144 since the recesses 144 are small and have been filled with other elements such as the gate dielectric layer 150 and the work function layer 152. However, embodiments of the disclosure are not limited thereto. In some other embodiments, a portion of the conductive filling 154 extends into the recesses 144, especially for the lower recesses 144 that may have larger space.

As shown in FIG. 3K, the isolation structure 137A₁ extends exceeding opposite sidewalls of one of the epitaxial structures 138 (such as the middle one), in accordance with some embodiments. In some embodiments, the isolation structure 137A₁ further extends along the bottom of the epitaxial structures 138. In some embodiments, the entirety of the epitaxial structure 138 is above the bottom surface of the isolation structure 137A₁. In some embodiments, the isolation structure 137A₁ further extends between the semiconductor fin 101A₁ and the metal gate stack 156A₂. In some embodiments, the isolation structure 137A₁ is in direct contact with the bottom of the epitaxial structures 138.

Due to the isolation structure 137A₁, leakage current from the epitaxial structure 138 may be blocked by the isolation structure 137A₁. Current leakage between the epitaxial structures 138 through the semiconductor fin and/or the semiconductor substrate 100 is thus prevented. The isolation structure 137A₁ may also help to reduce parasitic capacitance between the epitaxial structure 138 and the metal gate stack 156A₁ or 156A₂. Therefore, the operation speed and reliability of the semiconductor device structure may be improved.

As shown in FIG. 3K, each of the metal gate stacks 156B₁ and 156B₂ wraps around multiple semiconductor nanostructures 104 b′-104 d′, in accordance with some embodiments. Each of the metal gate stacks 156B₁ and 156B₂ is wider than each of the metal gate stacks 156A₁ and 156A₂. In some embodiments, each of the semiconductor nanostructures 104 b′-104 d′ that are wrapped around by the metal gate stacks 156B₁ or 156B₂ is wider than each of the semiconductor nanostructures 104 b′-104 d′ that are wrapped around by the metal gate stacks 156A₁ or 156A₂, as shown in FIG. 3K.

The device formed over the second region 20 may be a long channel (LC) device. In some embodiments, the isolation structures 137B₁ and 137B₁′ are separated from each other by one of the epitaxial structures 138, as shown in FIG. 3K. In some embodiments, the epitaxial structures 138 extend exceeding the bottom surfaces of the isolation structures 137B₁ and 137B₁′, as shown in FIG. 3K. In some embodiments, the epitaxial structures 138 are in direct contact with the semiconductor fin 101B₁. Current leakage between the epitaxial structures 138 through the semiconductor fin 101B₁ and/or the semiconductor substrate 100 may not occur since the epitaxial structures 138 over the second region 20 are separated from each other by a longer distance.

As mentioned above, in some embodiments, the ratio (T₃/T₄) of the thickness T₃ of the semiconductor layer 102 a to the thickness T₄ of the semiconductor layer 102 b is in a range from about 1 to about 2. In some cases, if the thickness ratio (T₃/T₄) is smaller than about 1, the semiconductor layer 102 a may be too thin. In the process illustrated in FIG. 3D, the semiconductor layer 102 a may not be able to be etched at a sufficient etching rate, which might make the subsequent processes hard to perform. In some other cases, if the thickness ratio (T₃/T₄) is greater than about 2, the semiconductor layer 102 a may be too thick. As a result, the recesses 133 illustrated in FIG. 3D or 2E may thus be too large. The spacer layer 134 illustrated in FIG. 3E may not be able to merge together. As a result the obtained isolation structures may have too many voids and/or seams, which might increase the risk of current leakage.

In some embodiments, the semiconductor layer 102 a (that functions as a sacrificial base layer) is completely removed during the formation of the recesses 132 used for containing the inner spacers 136, as shown in FIGS. 3C-3F. However, embodiments of the disclosure are not limited thereto. Many variations and/or modifications can be made to embodiments of the disclosure. In some other embodiments, the semiconductor layer 102 a is partially removed without being completely removed during the formation of the recesses 132.

FIGS. 4A-4E are cross-sectional views of various stages of a process for forming a semiconductor device structure, in accordance with some embodiments. As shown in FIG. 4A, a structure the same as or similar to that shown in FIG. 3C is formed or received.

As shown in FIG. 4B, similar to the embodiments illustrated in FIG. 3D, the semiconductor layers 102 b-102 d are laterally etched to form recesses 132, in accordance with some embodiments. In some embodiments, similar to the embodiments illustrated in FIG. 3D, the portions of the semiconductor layer 102 a under the dummy gate stacks 120A₁ and 120A₂ are completely removed to form the recesses 133. In some embodiments, the portions of the semiconductor layer 102 a under the dummy gate stacks 120B₁ and 120B₂ are partially removed without being completely removed, as shown in FIG. 4B. The remaining portions of the semiconductor layer 102 a form remaining structures 102 a′ that are surrounded by recesses 133′, as shown in FIG. 4B.

As shown in FIG. 4B, the semiconductor layer 104 a over the second region 20 has a first portion 104 a ₁ and a second portion 104 a ₂. The first portion 104 a ₁ is directly above the remaining structure 102 a′ and thus is prevented from being etched during the formation of the recesses 132. Therefore, in some embodiments, the first portion 104 a ₁ is thicker than the second portion 104 a ₂.

FIGS. 5A-5C are cross-sectional views (or plane views) of various stages of a process for forming a semiconductor device structure, in accordance with some embodiments. In some embodiments, FIG. 5A is a cross-sectional view (or a plane view) of the structure taken along the line A-A in FIG. 4B. FIGS. 6A-6C are cross-sectional views (or plane views) of various stages of a process for forming a semiconductor device structure, in accordance with some embodiments. In some embodiments, FIG. 6A is a cross-sectional view (or a plane view) of the structure taken along the line A-A in FIG. 4B.

In some embodiments, the remaining structure 102 a′ has substantially straight edges, as shown in FIG. 5A. In some other embodiments, the remaining structure 102 a′ has curved edges, as shown in FIG. 6A.

Afterwards, the processes the same as or similar to those illustrated in FIGS. 3E-31 are performed to the structure shown in FIG. 4B, in accordance with some embodiments. As a result, the structure shown in FIG. 4C is formed.

As shown in FIG. 4D, similar to the embodiments illustrated in FIG. 3J, the dummy gate dielectric layer 116 and the semiconductor layers 102 b-102 d (that function as sacrificial layers) are removed to form the recesses 144, in accordance with some embodiments. The remaining structures 102 a′ are also removed. Due to the removal of the remaining structures 102 a′, the recesses 144 penetrate through the isolation structures 137B₁ and 137B₁′ to expose the semiconductor fin 101B₁.

In some embodiments, FIG. 5B is a cross-sectional view (or a plane view) of the structure taken along the line B-B in FIG. 4D. In some embodiments, the isolation structure 137B₁ has substantially straight edges and surrounds the recess 144, as shown in FIG. 5B.

In some embodiments, FIG. 6B is a cross-sectional view (or a plane view) of the structure taken along the line B-B in FIG. 4D. In some embodiments, the isolation structure 137B₁ has curved edges and surrounds the recess 144, as shown in FIG. 6B.

As shown in FIG. 4E, similar to the embodiments illustrated in FIG. 3K, the metal gate stacks 156A₁, 156A₂, 156B₁, and 156B₂ are formed, in accordance with some embodiments. In some embodiments, each of the metal gate stacks 156B₁, and 156B₂ has a protruding portion that penetrates into the isolation structure 137B₁ or 137B₁′, as shown in FIG. 4E. In some embodiments, the protruding portion of the metal gate stacks 156B₁, and 156B₂ penetrate through the isolation structure 137B₁ or 137B₁′. In some embodiments, the metal gate stacks 156B₁ and 156B₂ are in direct contact with the semiconductor fin 101B₁. For example, the gate dielectric layer 150 or the interfacial layer (not shown) below the gate dielectric layer 150 is in direct contact with the semiconductor fin 101B₁.

In some embodiments, FIG. 5C is a cross-sectional view (or a plane view) of the structure taken along the line C-C in FIG. 4E. In some embodiments, the isolation structure 137B₁ has substantially straight edges and surrounds the metal gate stack 156B₁, as shown in FIG. 5C. The interface between the protruding portion of the metal gate stack 156B₁ and the isolation structure 137B₁ may be substantially straight.

In some embodiments, FIG. 6C is a cross-sectional view (or a plane view) of the structure taken along the line C-C in FIG. 4E. In some embodiments, the isolation structure 137B₁ has curved edges and surrounds the metal gate stack 156B₁, as shown in FIG. 6C. The interface between the protruding portion of the metal gate stack 156B₁ and the isolation structure 137B₁ may be curved. In some embodiments, the interface is a convex surface that faces an inner portion of the protruding portion of the metal gate stack 156B₁, as shown in FIG. 6C.

In some embodiments, each of the metal gate stacks 156A₁, 156A₂, 156B₁, and 156B₂ includes the conductive filling 154, as shown in FIGS. 3K and 4E. However, embodiments of the disclosure are not limited thereto. Many variations and/or modifications can be made to embodiments of the disclosure. In some other embodiments, some of the metal gate stacks are not large enough to contain the conductive filling 154.

FIG. 7 is a cross-sectional view of a semiconductor device structure, in accordance with some embodiments. As shown in FIG. 7, a structure similar to the structure shown in FIG. 3K is formed. In some embodiments, the trenches used to contain the metal gate stacks 156A₁ and 156A₂ have a narrow width. As a result, there may be no sufficient space for containing the conductive filling 154. The work function layer 152 may fill the remaining space of the trench during the formation of the metal gate stacks 156A₁ and 156A₂. In some embodiments, the trenches used to contain the metal gate stacks 156B₁ and 156B₂ have sufficient space for containing the conductive filling 154. Therefore, similar to the metal gate stacks 156B₁ and 156B₂ shown in FIG. 3K, the metal gate stacks 156B₁ and 156B₂ shown in FIG. 7 still have the conductive filling 154.

FIG. 8 is a cross-sectional view of a semiconductor device structure, in accordance with some embodiments. As shown in FIG. 8, a structure similar to the structure shown in FIG. 4E is formed. In some embodiments, the trenches used to contain the metal gate stacks 156A₁ and 156A₂ have a narrow width. As a result, there may be no sufficient space for containing the conductive filling 154. The work function layer 152 may fill the remaining space of the trench during the formation of the metal gate stacks 156A₁ and 156A₂. In some embodiments, the trenches used to contain the metal gate stacks 156B₁ and 156B₂ have sufficient space for containing the conductive filling 154. Therefore, similar to the metal gate stacks 156B₁ and 156B₂ shown in FIG. 4E, the metal gate stacks 156B₁ and 156B₂ shown in FIG. 8 still have the conductive filling 154.

Many variations and/or modifications can be made to embodiments of the disclosure. FIG. 9 is a cross-sectional view of a semiconductor device structure, in accordance with some embodiments. In some embodiments, a structure similar to the structure shown in FIG. 3K is formed. In some embodiments, the epitaxial structures 138 are formed using an epitaxial growth process. In the epitaxial growth process under some conditions, the semiconductor material may tend to be grown on the surfaces of elements made of a semiconductor material such as the surfaces of the edge elements 105 b-105 d. The semiconductor material may not tend to be grown on the surface of the isolation structure 137A₁. As a result, voids V are formed between the epitaxial structures 138 and the isolation structure 137A₁, as shown in FIG. 9 in accordance with some embodiments.

FIG. 10 is a cross-sectional view of a semiconductor device structure, in accordance with some embodiments. In some embodiments, a structure similar to the structure shown in FIG. 4E is formed. In some embodiments, similar to the embodiments illustrated in FIG. 9, voids V are formed between the epitaxial structures 138 and the isolation structure 137A₁, as shown in FIG. 10 in accordance with some embodiments.

Many variations and/or modifications can be made to embodiments of the disclosure. FIG. 11 is a cross-sectional view of a semiconductor device structure, in accordance with some embodiments. A structure similar to the structure shown in FIG. 3K is formed. In some embodiments, the spacer layer 134 may not be able to completely fill the recesses 133. As a result, one or more seams S may be formed in the isolation structures 137B₁ and/or 137B₁′, as shown in FIG. 11 in accordance with some embodiments.

Many variations and/or modifications can be made to embodiments of the disclosure. FIG. 12 is a cross-sectional view of a semiconductor device structure, in accordance with some embodiments. A structure similar to the structure shown in FIG. 3K is formed. In some embodiments, similar to the embodiments illustrated in FIG. 11, one or more seams S′ may be formed in the isolation structures 137A₁, as shown in FIG. 12. In some embodiments, the seam S in the isolation structures 137B₁ or 137B₁′ is larger than the seam S′ in the isolation structures 137A₁.

Embodiments of the disclosure form a semiconductor device structure with an isolation structure between a channel structure and a substrate. The channel structure is wrapped around by a gate stack. For example, the semiconductor device structure includes a stack of multiple channel structures that are wrapped around by a metal gate stack. Epitaxial structures are formed adjacent to the channel structures. The isolation structure further extends exceeding opposite sidewalls of the epitaxial structures. Current leakage from the epitaxial structures is thus blocked by the isolation structure. The performance and reliability of the semiconductor device structure are greatly improved.

In accordance with some embodiments, a semiconductor device structure is provided. The semiconductor device structure includes a semiconductor fin over a substrate and multiple semiconductor nanostructures suspended over the semiconductor fin. The semiconductor device structure also includes a gate stack extending across the semiconductor fin, and the gate stack wraps around each of the semiconductor nanostructures. The semiconductor device structure further includes a first epitaxial structure and a second epitaxial structure sandwiching the semiconductor nanostructures. Each of the first epitaxial structure and the second epitaxial structure extends exceeding a top surface of the semiconductor fin. In addition, the semiconductor device structure includes an isolation structure between the semiconductor fin and the gate stack. The isolation structure further extends exceeding opposite sidewalls of the first epitaxial structure.

In accordance with some embodiments, a semiconductor device structure is provided. The semiconductor device structure includes multiple channel structures suspended over a substrate. The semiconductor device structure also includes a gate stack wrapping around the channel structures. The semiconductor device structure further includes a first epitaxial structure and a second epitaxial structure each connecting the channel structures. Each of the first epitaxial structure and the second epitaxial structure extends exceeding a bottom surface of the gate stack. In addition, the semiconductor device structure includes an isolation structure between the channel structures and the substrate. An entirety of the first epitaxial structure is above a bottom surface of the isolation structure.

In accordance with some embodiments, a method for forming a semiconductor device structure is provided. The method includes forming a fin structure over a substrate. The fin structure has a sacrificial base layer and a semiconductor stack over the sacrificial base layer. The semiconductor stack has multiple sacrificial layers and multiple semiconductor layers laid out alternately. The method also includes forming a dummy gate stack to wrap around a portion of the fin structure. The method further includes partially removing the fin structure to form a first recess exposing side surfaces of the semiconductor layers and the sacrificial layers. In addition, the method includes partially or completely removing the sacrificial base layer to form a second recess between the semiconductor stack and the substrate. The method includes forming an isolation structure to fill the second recess and forming an epitaxial structure in the first recess. The method also includes removing the dummy gate stack and the sacrificial layer to release multiple semiconductor nanostructures made up of remaining portions of the semiconductor layers. The method further includes forming a metal gate stack to wrap around each of the semiconductor nanostructures.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A method for forming a semiconductor device structure, comprising: forming a fin structure over a substrate, wherein the fin structure has a sacrificial base layer and a semiconductor stack over the sacrificial base layer, and the semiconductor stack has a plurality of sacrificial layers and a plurality of semiconductor layers laid out alternately; forming a dummy gate stack to wrap around a portion of the fin structure; partially removing the fin structure to form a first recess exposing side surfaces of the semiconductor layers and the sacrificial layers; at least partially removing the sacrificial base layer to form a second recess between the semiconductor stack and the substrate; forming an isolation structure to fill the second recess; forming an epitaxial structure in the first recess, wherein the isolation structure extends along a bottom of the epitaxial structure; removing the dummy gate stack and the sacrificial layers to release a plurality of semiconductor nanostructures made up of remaining portions of the semiconductor layers; and forming a metal gate stack to wrap around each of the semiconductor nanostructures.
 2. The method for forming a semiconductor device structure as claimed in claim 1, further comprising: partially removing the sacrificial layers from the side surfaces of the sacrificial layers to form a plurality of third recesses after the first recess is formed; forming an inner spacer layer to fill the third recesses; and partially removing the inner spacer layer such that remaining portions of the inner spacer layer in the third recesses form a plurality of inner spacers.
 3. The method for forming a semiconductor device structure as claimed in claim 2, wherein the inner spacer layer also fills the second recess, and a second remaining portion of the inner spacer layer filling the second recess forms the isolation structure after the partial removal of the inner spacer layer.
 4. The method for forming a semiconductor device structure as claimed in claim 1, wherein the sacrificial base layer is completely removed.
 5. The method for forming a semiconductor device structure as claimed in claim 1, further comprising: forming a second fin structure over the substrate, wherein the second fin structure has a second sacrificial base layer and a second semiconductor stack over the second sacrificial base layer, the second semiconductor stack has a plurality of second sacrificial layers and a plurality of second semiconductor layers laid out alternately, and the second semiconductor stack is wider than the semiconductor stack; forming a second dummy gate stack to wrap around a portion of the second fin structure; partially removing the second fin structure to form a fourth recess exposing side surfaces of the second semiconductor layers and the second sacrificial layers; at least partially removing the second sacrificial base layer to form a fifth recess between the second semiconductor stack and the substrate; and forming a second isolation structure to fill the fifth recess.
 6. The method for forming a semiconductor device structure as claimed in claim 5, wherein the sacrificial base layer and the second sacrificial layer are at least partially removed simultaneously.
 7. The method for forming a semiconductor device structure as claimed in claim 6, wherein the sacrificial base layer is completely removed, and the second sacrificial base layer is partially removed.
 8. The method for forming a semiconductor device structure as claimed in claim 7, further comprising: removing the second dummy gate stack and the second sacrificial layers to release a plurality of second semiconductor nanostructures made up of remaining portions of the second semiconductor layers, wherein the semiconductor nanostructures and the second semiconductor nanostructures are formed simultaneously; and forming a second metal gate stack to wrap around each of the second semiconductor nanostructures.
 9. The method for forming a semiconductor device structure as claimed in claim 8, wherein the second sacrificial base layer is completely removed during the formation of the semiconductor nanostructures and the second semiconductor nanostructures.
 10. The method for forming a semiconductor device structure as claimed in claim 6, wherein the sacrificial base layer and the second sacrificial layer are completely removed.
 11. A method for forming a semiconductor device structure, comprising: forming a fin structure over a substrate, wherein the fin structure has a sacrificial base layer and a semiconductor stack over the sacrificial base layer, and the semiconductor stack has a plurality of sacrificial layers and a plurality of semiconductor layers laid out alternately; forming a dummy gate stack to wrap around a portion of the fin structure; partially removing the fin structure to expose side surfaces of the semiconductor layers, the sacrificial layers, and the sacrificial base layer; replacing at least a portion of the sacrificial base layer with an isolation structure; forming an epitaxial structure adjacent to the side surfaces of the semiconductor layers, wherein the isolation structure extends across opposite sidewalls of the epitaxial structure; removing the dummy gate stack and the sacrificial layers to release a plurality of semiconductor nanostructures made up of remaining portions of the semiconductor layers; and forming a metal gate stack to wrap around the semiconductor nanostructures.
 12. The method for forming a semiconductor device structure as claimed in claim 11, further comprising: partially removing the sacrificial layers from the side surfaces of the sacrificial layers to form a plurality of first recesses; and at least partially removing the sacrificial base layer to form a second recess, wherein the second recess is deeper than each of the first recesses.
 13. The method for forming a semiconductor device structure as claimed in claim 12, wherein the partial removal of the sacrificial layers and the at least partial removal of the sacrificial base layer are performed simultaneously using a same etching process.
 14. The method for forming a semiconductor device structure as claimed in claim 12, further comprising: forming a dielectric layer to fill the first recesses and the second recess; and partially removing the dielectric layer such that first remaining portions of the dielectric layer in the first recesses form a plurality of inner spacers, and a second remaining portion of the dielectric layer forms the isolation structure.
 15. The method for forming a semiconductor device structure as claimed in claim 11, further comprising removing a remaining portion of the sacrificial base layer during the removal of the dummy gate stack and the sacrificial layers.
 16. A method for forming a semiconductor device structure, comprising: forming a first fin structure and a second fin structure over a substrate, wherein the first fin structure has a plurality of sacrificial layers and a plurality of semiconductor layers laid out alternately, and widths of the second fin structure and the first fin structure are different from each other; forming a dummy gate stack to partially cover the first fin structure; forming a first isolation structure between the first fin structure and the substrate; forming a second isolation structure between the second fin structure and the substrate, wherein the first isolation structure and the second isolation structure are physically separated from each other, and the first isolation structure and the second isolation structure are formed simultaneously; removing the dummy gate stack and the sacrificial layer to form a plurality of semiconductor nanostructures made up of remaining portions of the semiconductor layers; and forming a metal gate stack to wrap around the semiconductor nanostructures.
 17. The method for forming a semiconductor device structure as claimed in claim 16, further comprising: forming a sacrificial base layer over the substrate, wherein the first fin structure is formed over the sacrificial base layer; partially removing the sacrificial layers from side surfaces of the sacrificial layers to form a plurality of first recesses; at least partially removing the sacrificial base layer to form a second recess between the substrate and the fin structure; forming a dielectric layer to overfill the first recesses and the second recess; and partially removing the dielectric layer such that first remaining portions of the dielectric layer form inner spacers covering edges of the sacrificial layers, and a second remaining portion of the dielectric layer forms the isolation structure.
 18. The method for forming a semiconductor device structure as claimed in claim 17, wherein the sacrificial base layer is completely removed.
 19. The method for forming a semiconductor device structure as claimed in claim 17, wherein a remaining portion of the sacrificial base layer is removed during the removal of the dummy gate stack and the sacrificial layer.
 20. The method for forming a semiconductor device structure as claimed in claim 16, wherein the second recess is deeper than each of the first recesses. 